The neural crest is a vertebrate innovation, sometimes referred to as the fourth germ layer;the neural crest gives rise to migrating cells that differentiate into cartilage, melanocytes, the peripheral nervous system, and the outflow tract of the heart. Defects in the neural crest are involved in over 400 human syndromes and result in craniofacial, heart, pigmentation, peripheral and central nervous system defects. Our focus has been on the environmentally regulated and developmentally important transcription factor NFKB and its regulatory targets in the early embryo. NFKB activation has been implicated in the teratogenic effects of environmental factors such as ethanol. Early embryonic defects impacting the neural crest underlie the neurological, craniofacial, and dental malformations associated with Fetal Alcohol Syndrome (FAS) and the less severe, but still significant alcohol-related neurodevelopmental disorder (ARND) and alcoholrelated birth defects (ARBD). The goal of this proposal is to better understand the molecular nature of these defects, particularly those involving the regulatory targets of NFKB. Using the clawed frog Xenopus as a model system, we found that NFKB regulates the levels of twist, snai/1, and snai/2(slug) RNA levels. twist encodes a bHLH transcription factor, while snai/1 and snai/2 encode the related zinc-finger transcription factors Snail1 and Snail2;these three transcription factors are also implicated tumor metastasis. In the early embryo, Twist, Snail1, and Snail2 regulate one another's expression and are required for the formation of mesoderm and the subsequent formation, survival, and differentiation of the neural crest. Surprisingly, can rescue each other's loss of function phenotypes. There is evidence that a similar network of interactions may be active in the early mouse embryo, arguing for the relevance of this system to human embryonic/neural crest defects. In light of the shortened (2 year) timespan available for this project, we will concentrate our efforts on two revised aims and will delay our comparative and cell migration studies using ebrafish until a later time. By exploiting the experimental strengths of the X. laevis system we will i) define the unique and complementary mesodermal roles of twist, snai/1, and snai/2 on neural crest induction, survival, and differentiation and ii) identify the temporal and spatial requirement for mesodermal signals in neural crest specification. Together these observation should have important implications for understanding the behavior of molecular and inductive networks in general and the prevention and/or amelioration of neural crest defects in particular.